Quadruple-label experiments, involving an extravascular, extracellular, permeant nonmetaboliz-able and permeant metabolizable glucose tracers, have been performed in the human forearm (with insulin clamped at different levels) and myocardium (in different heart working conditions). The aim of these studies is to assess the extent to which glucose transport and metabolism in vivo are influenced in the forearm by different levels of insulin and in the myocardium by different heart beating rates. Experimental results will be analyzed using the compartmental and the distributed models approach, and a comparison will be attempted between the results obtained with each meth-od. Specific Aims: 1. To develop a mathematical model of capillary-tissue exchange suitable for analysis of the experimental results; 2. To determine the transport and metabolism of glucose in human muscle tissue, and its control by insulin, using the multiple indicator dilution technique. 3. To derive a measure of a posteriori numerical identifiability of distributed model parameters.